Old JD 50V saw; won't run long

[jdsawguy]

I have a circa late 70's John Deere 50V (Echo CS-452) chainsaw that I have used off and on since buying it new. One day it just stopped running. After taking the carb apart I saw that the round filter screen was plugged with what looked like saw dust. I rebuilt the carb and attempted to start the saw. At best it runs very rough for no longer than 30 seconds. I have noticed that fuel seemed to be coming out of the muffler so I thought the metering lever might be mis-adjusted. I checked and it is level with the carb interior as required. I have fiddled with the Hi & Lo needle adjustments, inspected the seats and needle ends, I have looked in the metering hole (clean) and installed a new valve there. I also have cleaned out all the little passages. Saw still runs terrible and only for about 30 seconds. It will not spool up when the throttle is opened. Fuel still seems to be leaking out of muffler. While running it is very smoky.

Any ideas? I just love this old saw and long to use it again.

 

[Fish]

The points could be dirty causing the trouble, get a new plug and check the spark.

 

[epicklein22]

Hmmm, it sounds like you have done quite a bit of problem solving. The gas coming out of the muffler sounds like you jets are too rich. Screw the jets in all of the way and then back them out 1 full turn. I had a 031 that pumped out fuel out of the carb and the problem was the gas cap/vent. I changed the cap and the problem was solved. The vent was sealed off and was creating pressure and pumping gas through the line and dripping through the carb.

Hope this helps, there are some good mechanics here. I just wanted to get your thread higher up.

 

[blsnelling]

I had a 031 that pumped out fuel out of the carb and the problem was the gas cap/vent. I changed the cap and the problem was solved. The vent was sealed off and was creating pressure and pumping gas through the line and dripping through the carb.

Sounds like your problem is actually a leaky needle and seat in the carb. It's normal for a tank to build up pressure. The tank vent prevents a vacuum but allows pressure to build up. It sounds like your needle and seat weren't sealing enough to hold the pressure.

Have you ever pulled a fuel line off the carb and had it squirt across the room? Your needle and seat have to be able to hold that pressure without leaking.

 

[epicklein22]

Oh, it was shooting out like crazy. I tried a completely different carb and came up with the same results.

 

[jdsawguy]

I will check the fuel cap and points. I did screw the jets all the way in and then out to 1 1/4 turns like Walbro says. It started to run a little better as I screwed the low jet in to about 3/4 of a turn, but that was as good as it got. The spark plug is new. Maybe I need to re-inspect the metering lever, metering rod and the seat. Could be a little piece of junk got in there and it is holding the metering rod open.

This 'ol saw is heavy, but great for cutting to length for firewood. Very comfortable to run and good on fuel.

Great help so far. Thanks, Guys. This is a great site!!

 

[Fish]

OK, do this, dump out the fuel, start the saw and run it, as the last bit
of fuel is burned, the engine "should" speed up like crazy, if it doesn't,
then look at the points.

You can rule out the rich carb hypothesis that way.

 

[jdsawguy]

I will add this to the "to do" list.

BTW, why does a saw run up like that when it is about to run out of fuel? Always wondered.....

 

[Fish]

I will let the other guys tell you about it, I have a customer outside.

 

[teacherman]

I will add this to the "to do" list.

BTW, why does a saw run up like that when it is about to run out of fuel? Always wondered.....

The carb leans out and the saw runs like a hot rod for a moment. Much longer like that, and you'd hear a scraping sound and get a good score! (on the piston) generally considered to be a bad thing............

 

[jdsawguy]

Ah, yes. Lots of air and little fuel means lean. Now I get it.

 

[Fish]

Running it a few seconds lean won't hurt, especially since your saw is
full of oil and mix.

With a fully adjustable carb, you can burn up a brand new saw in
about 45 seconds, by turning the high speed screw in=lean.

These engines will run at least 16,000 rpm, unless you richen them up
and slow it down to @ 12,000 - 13,000. When leaning them out, since the
fuel is less, so is the lubrication, so carb adjustment is critical on any saw.
But in your case, this is just a test, and will not hurt. If it did, one would need to rebuild the saw every time you ran out of gas.

But it is important to identify the problem, instead of throwing time and
money at it. This old saw probably topped out at @ 10,000 or so,
but this test will helpyou rule out a rich carb problem. Point ignition
problems can easily fool you into thinking it is fuel related, but this test
will let you know quickly.

 

[jdsawguy]

Emptied fuel and tried to start it. It ran for about 15 seconds, but did not race. Just died at a slow sputter. Still leaking gas out of the bottom of the muffler. Did not check gas cap yet. Took out plug and grounded it against block. It is getting plenty of spark. Plug was very wet.

That is enough for tonight. Will try again tomorrow. I appreciate your help.

 

[Fish]

Plenty, plenty weak spark can be the problem.







No revving when running out of fuel....................MMMMMMMMMM

Makes me think the problem is somewhere else................


Compression????

Ignition??

I dunno, I am stumped...................................

Anyone???????

 

[stihltech]

fuel

I checked the posts so far. Did you check and/or change the fuel filter and line in the tank?

 

[PES+]

The diaphram order

Are you certain you installed the diaphrams in the correct order?

The fuel pump diaphram goes against the flat carb body and the gasket goes between the cover and the diaphram.

The metering side (the one with the rivet in the diaphram) goes gasket against the carb body then diaphram then cover.

 

[jdsawguy]

The first thing I did was to replace the in-tank fuel line and filter. I did an ad hoc pressure test of the fuel line from the tank to the carb and it did not seem to leak.

What is the acceptable gap between the flywheel and the ignition module (not sure of that is what you call it)?

Can a digital meter catch the voltage value at the spark plug cable when the start rope is pulled? If so, what should the value be?

Thanks again.

 

[jdsawguy]

I followed the Walbro diagram for gasket installation so I think they are installed as you have outlined. Thanks.

 

[jdsawguy]

I took the carb off again for the umpteenth time and bent the metering arm lever a little so as to not open the rod as much. Put it all back together. Saw runs a little better and does not stall, but it is still spitting gas and idling very rough.

I noticed that when adjusting the lo speed jet it turned very hard. I wonder if I cross threaded the screw and it is not actually seated all the way into the bore hole? This is allowing all the extra fuel as suggested by one poster earlier?

My next step is to take the carb off again and check the threads of the lo speed jet. It is a long shot, but does any one know the thread pitch for this?

Thanks

 

[jdsawguy]

I hope I have not lost you guys......

I am now convinced that I stripped the threads of the lo speed jet. I have screwed it in as far as I can yet the saw will now run. I can now get it to idle non-stop, but it will not spool up when I squeeze the throttle. It seems to balk or bog down. It is still dripping gas out the muffler, but not as much. Still smokes like crazy too.

The needle itself looks intact, but the threads in the bore look boogered.